In cytology, there is an ever-increasing demand for automatic cellular counting, volumetric differentiation and analysis. At the present time, screening of cytological material such as for the detection of cancerous or malignant cells, and for sizing and counting the cells present in a particular amount of material, is typically manually accomplished by a two level screening process. The cells are first prescreened visually by an observer capable of determining which samples apparently contain abnormal cells and to determine the size cell one hopes to count within a sample. The abnormal cell-containing samples are then examined by a trained cytotechnologist or pathologist who makes a final determination as to whether the cells of these samples are indeed cancerous. This method fairly accurately finds cancerous cells but it has a number of disadvantages. First, it is slow, requiring considerable technician time. Second, it is costly due to the human time involved. Third, it is nonquantitative in that the criteria of abnormality as well as the amount of cells present in a particular volumetric sample are primarily subjective. Because of the time and costs involved, it is generally not practicable to examine large populations of individuals using these prior art techniques.
In addition, most of the cellular specimens examined by a medical laboratory are normal. Therefore, the level of alertness and interest of those who do the screening is difficult to maintain. For example, in cytological examination for uterine cervical carcinoma, 98% of the women examined do not have cancer. Thus, personnel turnover may tend to be high and the test results become less quantitative and more costly.
Recently systems have been developed for automatically determining the volumetric distribution of a sample of cells. The output can be used, for example, to normalize light signals from a cell analyzer such as that disclosed in the U.S. Pat. No. 3,824,402 to Mullaney et. al. issued July 16, 1974.
A typical electrical analysis device utilizes orifices having electrodes at either end disposed in the surrounding solution or, disposed within the orifice itself as in U.S. Pat. No. 3,924,180 issued Dec. 2, 1975 to Salzman et al. In either case, the system must be calibrated from time to time.